Electromagnetic instrument



May 12, 1931. A. A. THOMAS 1,804,961

ELECTROMAGNETI C INSTRUMENT Filed Oct. 12, 1928 Patented May 12, 1931 sire assassi- ADOLPH A. THOMAS, 015 NEW YORK, N. Y.

ELECTROMAGNETZC INSTRUMENT Application filed October 12, 1928. Serial No. 312,093..

This invention relates to electromagnetic translating devices, and its object .isto pro vide an instrumentin which a vibratory armature is supported by elastic pressure means. In a preferred form of my invention, the ends of the armature engage elastic pads held in pressure contact with opposite sides of the armature, whereby the latter is resiliently suspended in balanced position and is capable of vibrating in two ways. One practical advantage of this construction is the use of my device as an electric phonographreproducer for playing lateral-cut and vertical-cut records. In other words, the elastic mounting of the armature permits the latter to vibrate laterally for lateralcut records and vertically, for vertical-cut records. No adjustment of the reproducer on its supporting arm is necessary.- A stylus holder connected to the armature is adapted to receive a suitable stylus for playing either type of record. For Edisonrecords',the

. stylus holder is preferably provided with a 25, diamond point permanently embedded there,

in. V

The foregoing and other objects and advantagesjof my inventionwill be fullyf understood from a detailed description ofthe accompanying drawings, in'which- V Fig. 1 shows a front view of an; electric phonograph reproducer embodying invention, the cover being removed from the ca i g; I

Fig. 2 is a section on line 2-2 of Fig. 1; Fig. 3 is an enlarged section through the armature and its elastic mounting;

Figs. 4 and 5 are views similar to Fig. 3, but showing modified arrangements. of the elastic pressure pads between WhlCll'lZllG armature is supported; 7

Fig. 6 shows a perspective of the recessed ends of the pole pieces used-in the construe-T tion of Figs. 14; V

Fig. 7 shows a perspective of the recessed end of a modified form'of pole piece; and Figs. 8, 9 and 10 show fragmentarypere spective views of different forms of recessed armature ends for engaging the elastic sup;- porting pads i i other nonmagnetic materials suitable for Referring to Figs. 1 and 2, the operative parts of the instrument are mounted in a suitable casing 10 supported on the free end of an arm 12, which is supposed to be pivoted at its other endffor horizontal swing- 5 ing movement over a record. The casing 10 may have a hub or cylindrical extension 13 adapted'to fit over the free end of arm 12', which may be a light tube of brass, aluminum and the like, and a set-screw 14 or. other means secures the casing in fixed position on-the supporting arm. The casing 10 may be stamped out of sheet metal, or it may be a casting of aluminum, brass, bakelite' and;

that purpose. The front of casing 10 car ries a removable cover 15, which may conveniently be held in place by screws 16 entering holes 17 in the casing. The cover may be of the same materialasthe casing and suitably ornamented, if desired.

A permanent magnet 18 is mounted in casing 10, being rigidly held in position by screws, bolts or'rivets' 19, or in any otherv practical way. To allow for any unevenness in the contour of the magnet and easing, the magnet is preferably spaced from the adjacent wall of the casing which it engages only along the projections 20 and 21. By making the magnet ofsubstantially thesame shape as the'casing, it is possible to house a magnet, ofconsiderable length in a small space.- The magnet 18 is made of good magnet steel, either solid or laminated. A pair of bifur- 'cated pole pieces 22 and 22 are secured to the ends of'magnet 18 by fastening members 23, which may be screws, bolts, rivets and the like. Each pole piece has apair of limbs or bifurcations marked'24 -25 and 24-25 respectively. In'the particular construction illustrated, these four polar limbsterminate in projections indicated respectively by 26-27 and 262' Z. The oppositely aligned polar projections 26-,27 form an airgap 28, and'the two other polar projections 26"27 form an airgap 29. At least one of the pole pieces carries a coil 30, whichin this instance is mounted on polar limb 24, although it may be supported in any other operatlve position,

A pin 31, or other suitablemeans, holds the coil in fixed position on the pole piece. The conductors 32, which may conveniently be led through the hollow supporting arm 12, connect the coil 30 in a suitable circuit adapted to convert electric impulses into sound. Since amplifying systems for radio and phonograph loudspeakers are well known, it will not be necessary to illustrate or describe any particular loudspeaker system associated with coil 30.

An armature 33, consisting of a rigid magnetic bar, is resiliently supported at its ends by means of two pairs of elastic pads 34, which are preferably blocks of rubber. In Figs. 1 and 3, the pads 34 are connected to the ends of armature 33 by screws or pins 35 which pass through holes 36 (see Fig. 8) near the ends of the armature. The polar limbs of pole pieces 22 and 22' are provided with recesses 37 (see Figs. 3 and 6) for receiving the elastic pads 34 in a tight fit, whereby displacement of the pads is positively prevented. If necessary or desirable, the ends of the armature bar 33 may be reduced in thickness to provide shoulders 38 against which thepads are held in pressure contact. Any other practical means may be used for holding the elastic pads 34 firmly in supporting position between the pole pieces and the armature to prevent axial or twisting movement of the latter. The relative arrangement and proportions of the parts are such that, when the pads 34 are inserted in the recesses 37 of pole pieces 22 and 22', they are compressed and remain under compression to form a universal elastic mounting for the armature.

A stylusholder 39 is connected to the center-of armature 33 by a pin 40, or in-any other practical way. In other words, the stylus holder 39 is directly mounted on and supported. entirely by the vibratory armature 33. In the broad aspect of my invention, the

Stylus holder 39 may be of any suitable construction for carrying one or more stylus members adapted to play lateral-cut records and vertical-cut records. For playing vertical-cut records of the Edison type, thestylus holder 39 has a stylus point 41, which may be a diamond point or similar member permanently embedded in the stylus holder. For playing lateral-cut records, the stylus holder 39 has a hole 42 adapted to receive a removable needle 43, which is clamped in playing position by a set-screw 44 projecting forwardly of the cover 15. A slot or opening 45' at the bottom of cover 15 allows the setscrew 44 to pass therethrough. The casing 43 will drag over the record at the proper angle, as is usual in phonographs. On the other hand, the entire pickup may be mounted in slanting position on the arm 12, in which case the needle hole 42 may extend substantially parallel with the sides of the casing. Lateral-cut records of the Victor type are usually played with a pointed steel needle. To play vertical-cut records of the Pathe type, the stylus 43 preferably terminates in a rounded point, which is usually a tiny ball of sapphire, or other hard mineral. It is thus seen that the stylus holder 39 is so constructed as to be capable of playing three different kinds of records, it being only necessary that the proper stylus is inserted; in the hole 42. The stylus 41 is permanently mounted in the holder for playing Edison records only.

By referring to Fig. 2, it will be noticed that the playing points of the stylus members 41 and 43 are in'a vertical line or plane 47 passing substantially through the center of armature 33, so that the vibrations of the stylus holder 39 when playing eithertype of record are directly communicated to the armature 33 without lateral twisting movement of the armature. While this arrangement is not absolutely essential, it has its practical advantages. In Figs. 1 and 2, the line 48 represents diagrammatically the playing surface of a disk record. Of course, either of the stylus members 41 and 43-may beomitted, if desired. For instance, if the pickup is 'to'be used only on lateral-cut rec ords, there would be no need of stylus 41. On the other hand, if the pickup is intended for playing Edison records only, the stylus 43'is superfluous. However, the most prac:

tical embodiment of my invention as a pickup contemplates the playing of both. types of record.

The operation of the universal pickup shown in Figs. 1-3, will be clear from the preceding description, and it will therefore be sufficient if I summarize it in a few sentences. When the stylus-member 43 operates on a lateral-cut record, the armature bar 33 is oscillated about an imaginary central pivot diagrammatically indicated at 49, whereby the ends of the armature alternately approach the polar projections 2627 and 2627. In the first named position of the armature, most of the flux passes through the polar limbs 24 and 25; while in the second position of the armature, the polar limbs, 25 and 24 carry most of the flux. Consequently, the lateral or oscillatory movements of armature 33 about the imaginary central pivot 49 produce flux variations in coil. 30, and these variations in turn generate electric impulses which are utilized to operate loudspeaker mechanism.

When the stylus holder 39 is vibrated vertically by the stylus point 41 in playing vertical-cut records of the Edison type, or by the stylus member 43 in playing vertical-cut records of the Pathe type, the armature bar 33 is moved up and down in such a way that its endsalternately approach the polarprojections 2626' and the polar projections 2727. When the armature moves up toward the polar projections 26-26, most of the field flux passes through the polar limbs 24 and 24'; when thearmature 33 moves down toward the polar projections 27 -27, most of the flux passes through the polar limbs 25 and 25. These vertical bodily movements of armature 33 produce flux variations and therefore electric impulses in coil 30, and these impulses are electrical representations of the vertical-cut spiral groove of the record.

The elastic pads 34 permit the two kinds of movement of'armature equally well for playing lateral-cut and vertical-cut records, and these pads thus constitute aresilient universal mounting for the armature. An additional inherent function of the elastic pads 34 is their damping action by which they a1- ways tend to restore the armature to normal balanced position. That is to'say, the armature vibrates only as actuated bythe stylus point, being without a fundamental frequency and having no parasitic vibrations. The elastic members 34, by virtue of their opposing pressures, are always ready to throw the armature back toneutral or stationary position. The airgaps, 28 and 29 need only be'very little wider than the thickness of the armature ends, because the move ments of the armature are exceedingly small.

Since the stylus'holder 39 is mounted directly on the armature, the microscopic movements of the stylus points are communicated to the armature without lost motion. of elasticity or resiliencyof the elastic supporting pads 34 is such that the armature responds instantly and correctly to the sinallest movement of the playing, stylus. the bifurcated pole pieces 22 and 22 provide two parallel paths for the magnetic flux,the vibratory movements'of armature 33 merely shift the flux from one parallel path to the other without causing any substantial variation of the flux through the steel body of the permanent -magnet 18. This increases the sensitiveness and efficiency of the instrument,

particularly if the pole pieces 2222 and the armature 33 are made of magnetic material (solid or laminated) having higher mag netic permeability than the field magnet 18 itself. Also, it shall be noted that normally the armature is balanced not only mechani cally by the elastic pads 34, but also magnetically by the opposing polar projections 26-27 and 26-27.

In Fig. 4 the elastic pads or blocks 34 are attached to the pole pieces by screws 50and the armature33 is provided with recesses 51 The degree Since for receiving the ends of'the pads. .Other-.

wise, what has been said for the construction and operation of Figs. 1, 2 and 3 is fully applicable to Fig. 4 without the need of repetition. really necessary, because thecubical pads 34 are held against displacement by the recesses 37 in the pole pieces and the recesses 51 in the armature. Since the pads 34 are inserted undercompression and remain compressed, they engage the edges or shoulders of the aligned recesses 37 and 51 in pressure contact, so that the pads are safely locked in place without the need of additional fasten ing means- 7 In Fig. 5 the elastic pads 34 are held in supporting position by screw-threaded polar extensions 52 mounted on the ends of polar limbs 2425'and 2425. By adjusting the polar projections 52, it is possible to reg11-,

late thenormal compression of the support:

ing pads 34. Fig. 9 shows the armature 33' provided at each end with a pair of recesses 3 for receiving the elastic supporting pads The only difference between Figs. 9 and 10 is that in Fig. 10 the rectan ular recess 51 presents four retaining shoulders to the cubical pads 34, while in Fig. 9 the recesses 53 extend to the very .ends-of'the armature.

Thepolarprojections 26-27 and 26-.27

permit the airgaps 28 and29 to be made only ture ends operating in the airgaps, as will be clear'from Figs. 3 and4. This permits the use of pads 34 of considerable thickness to provide the requisite amount .of elasticity. In

a less efiicient form of my invention, the

polar projections 26- 27nnd 29- 27" may be dispensed w th, as shown i'nF1g..7, where each pole piece has a rectangular recess 54 Edison type, and for playing lateral-cut records and vertical-cut records of the 'Pathe type it is only necessary to insert the proper stylus in the hole 42 of the holder 39-. The parts comprising the instrument are fewand rugged, and are furthermore easily made and assembled. Strictly speaking, there is only one .movable part, which is the vibratory unit comprising the armature 33, the stylus holder 39 and the playing stylus '41 or The elastic pads 34 will last a very long time, but should they become worn or otherwise cease to'function properly, it is a simple boat- The fastening members 50 are not slightly wider than thethickness of the armater to insert new pads. Generally speaking, these pads will" last for years. When I refer to the elastic supporting i'nembers as pads, I use the term in its broadest possible sense to indicate any practical form of compressible elastic members adapted to act as a universal mounting for the armature. The

imaginary pivot point l9 for the armature 33 is not a fixed point but rather a variable fulcrum which automatically adjusts itself in the playing of lateral-cut records. The armature is supported at its ends by elastic pads which allow a certain amount of free play at the fulcrum point 49' and thereby improve the operation of the pickup.

It is hardly necessary to add that the relative proportions of the various parts have been purposely exaggerated to make the drawings as clear as possible. In the actual instrument, the parts are arranged much morecompactly, so that the pickup as a whole is a smallerunit than that illustrated'in the drawings. The weight of the pickup is so calculated (as determined by experiment) as toplace the proper amount of pressure on the stylus point to get the best results in any particular design of unit. If necessary, the pickup may be counterbalanced to the required extent in any practical way. These will be clear to those skilled the art without additional description and illu-"tration.

Although I have shown and described certain specific constructions, I want it understood that my invention is not limited to the details set forth. Changes and modifications will probably occur tot-hose skilled in the art without departing from the scope of the in vention as defined in the appended claims. It is evident that'the basic features of my invention may be used in electric translating instruments of other types and kinds than phonograph pickups, such as recording instruments. transmitters, receivers, and other devices utilizing a vibratory member to produce electric impulses or to be actuated in accordance with transmitted impulses.

I claim as my invention 1. An electric translating instrument com prising a magnet structure having pole pieces, an armature in operative relation to said pole pieces. elastic means in pressure contact with said armature on opposite sides thereof for supporting the armaturefor vibratory move ment about an intermediate fulcrum, a coil operatively associated with said armature, and an operative member connected to the co itral portion of said armature.

2. An electric translating instrument comprising a magnet structure having pole pieces, as armature in operative relation to said pole pieces, elastic pads in pressure contact with the ends of said armature on opposite sides thereof for supporting the armature for oscillatory movement'about an intermediate fulcrum, a coil operatively associated with said armature, and an operative member connected to the central portion of said armature.

3. In an electromagnetic translating instrument, an armature supported at its ends by and between elastic means held in opposing pressure contact with opposite sides of the armature, whereby said armature is capable of vibrating bodily with both ends moving in the same direction and oscillating about a central axis, and electromagnetic means. operat'ively associated with said armature.

at. In an electromagnetic translating instrument, a vibratory armature bar supported at its ends by compressible elastic means in pressure contact with opposite sides of the bar, said elastic means constituting the sole support for said bar, and an Operative member connected to the central portion of said bar.

5. In an electromagnetic translating instrument, the combination of a magnet having pole pieces, and a vibratory armature bar supported at each end by and between two compressible elastic pads held by said pole pieces in pressure contact with opposite sides of the bar, said elastic pads constituting the only means for supporting the armature bar for vibratory movement. I

' 6. In an electric phonograph reproducer, a stylus-holding; member supported on a uni versal mounting which permits said member to vibrate laterally for lateral-cut records and vertically for vertical-cut records, said mounting including compressible elastic means which constitutes the sole support for said armature.

'2'. An electric phonograph reproducer comprising avibratory armature supported at each end by and between two compressible elastic pads held in pressure contact with opposite sides of the armature, said elastic pad constituting the sole support for said armature, a stylus holder attachedto said armature which is capable of vibrating laterally for lateral-cut records and vertically for vertical-cut records. and electromagnetic means for converting the movements of said armature into electric impulses. I

8. In an electric phoi'iograph reproducer for selectively playing lateral-cutand vertical-cut records, electromagnetic mechanism having a vibratory armature carrying at its center a stylus holder adapted to play both kinds of records, and a universal mounting for said armature, said mounting including elastic means in pressure contact with opposite sides of the armature.

9. In an electric phonograph reproducer for selectively playing lateral-cut and vertical-cut records, electromagnetic mechanism having a vibratory armature carrying at its center a stylus holder adapted to play both kinds of records, and a universal mounting for said armature, said mounting-including elastic-pads inpressu're contact with the ends of said armature on opposite sides thereof.

10; An electric translating instrument comprising a magnet having two pairs of pole pieces forming two aligned airgaps, an armature projecting at its ends into said airgaps, elastic "means engaging said pole pieces and the ends of said armature on opposite sides thereof for supporting the armature for vibratory movement, said elastic means constituting the sole support for saidarmature,

anda coil operatively associated with said 12. An electric translating instrument 7 comprising a magnet having two pairs of pole pieces forming two aligned airgaps, anarmature projecting at its ends into said airgaps, elastic pads engaging said pole pieces and the ends of said armature on opposite sides thereof for supporting the armature for vibratory movement, a coil operatively associated with said armature, and means for locking said pads against displacement.

13. An electric translating; instrument comprising a magnet having two pairs of pole pieces forming two aligned airgaps, an armature projecting at its'ends into said airgaps, elastic pads engaging said pole pieces and the ends of said armature on opposite sides thereof for supporting the armature for vibratory movement, said pole pieces and armature having recesses in which said pads are seated and held against a coil mounted on one of said pole pieces.

14:. An electric phonograph reproducer comprising a magnetic structure having pole pieces, an armature inoperative relation to said pole pieces, a stylus holder connected to the central portion of said armature, elastic means in pressure contact with said armature on opposite sides thereof, whereby said armature vibrates vertically for vertical-cut recr a coil for converting the movements of ords and laterally for lateral-cut records, and said armatureinto electric impulses.

15. An electric phonograph reproducer comprising a magnetlc structure having pole pieces,

a stylus holder connected elastic pads held in pressure contact with the ends of said armature on opposite sides thereof, where-.

by said armature vibrates vertically for vertical-cut records and laterally for lateral-cut movement, said elastic means con-" displacement, and

a coil influenced by an armature in operative relation to gaging the lateral ends-of-saidunit to permit the same to oscillate about, the; center for -lateral-.cut records and vibrate vertically for vertical-cut records, and means: for converting the movements OfSRld unit into, electric impulses. V A

17 In an electric phonograph reproduced;

a substantially T shaped vibratory unit having stylus-holding means at its lower end for and a coil for converting the move-V selectively playing lateral-cut and verticalout records, lastic pads held incopposing pressure contact with; the lateral ends of said unit to permit the same to oscillate about the center for lateral-cut records and vibrate vertically for vertical-cut records, and means for converting the movements of "said unit into electric impulses; g V

18. An electric phonograph reproducer comprisinga magnet having two pairs of pole pieces forming two aligned airgaps, acoil mounted on at least one of said pole pieces, an armature projecting atits ends intosaid airgaps,a stylusholder connected to the center of "said aitrnature,

elastic pads engaging V the ends of said armature on opposite sides thereof, and means for holding said pads in pressurecontact with said armature,.which is thereby resiliently supported to vibrate vertically for vertical cut recordsand laterally for lateral-cut records.

19. In anfielectric'phonographreproducer,

a magnet having two pairs of pole pieces forming two horizontally aligned airgaps, an I armature extending at'its ends, into said air o gaps, afstylus holder connected :to the center of said armature, elastic means for support-' ing said armature so that it vibrates vertically meanspermitting the armature {to vibrate laterally about a'central pivot when the stylus holder is actuated by lateral-cut records, and

the vibrations o'fsaid ar I mature.

v with both ends movingin the same direct on when the stylus holder is' actuated by, vertical ciit records, 7 said elastic mounting 20. In" an electric "phonograph reproducer, a a magnet having two pairs of pole' pieces forming two horizontally aligned airgaps,

an armature extending at its ends into said opposite sides thereof in pressure" contact,

whereby said armature resiliently suspended at its ends to vibrate laterally about a central pivotfor lateral cut records, and

a stylus holder connected tothe centhe end portions of said 3 I ,for playing ends of said armature bar and constituting the-sole support therefor, and means for holding said pads compressed.

"22. An electric v phonograph repro-ducer' havin-gan armature supported at both endsto oscillate about a variable central fulcrum in the playing of lateral-cut records, a stylus holder connected to the central portion of armature, and electromagnetic means for converting the movements of said armature into electric impulses.

23. An electromagnetic phonograph reproducerhaving an armature provided with a universal mounting which permits vibration of said armature for playing lateral-cut and vertical-cut records, said universal mounting including compressible elastic means in pressure engagement with said armature. I

24. In an electric translating device, a magnet structure having a pair of airgaps, an armature projecting at its ends into said airgaps, compressible elastic means engaging the ends of said armature on opposite sides.

thereof to hold the same in predetermined normal position, said elastic means constituting the sole support for said armature, and a coil influenced by the movements of said armature.

25.. In an electric phonograph reproducer, an. armature having a universal elastic mounting to permit oscillatory movement of the armature about an intermediate fulcrum and bodily movement in the same direction at both ends, means for operating said armature in the playing of lateral-cut and vertical-cut records, and electromagnetic means for con venting the movements ofs aid armature into electric impulses. v

26. In an electric phonograph reproducer, asubstantially T-shaped vibratory unit having stylus-holding means at its lower end. elastic supporting means engaging thelateral ends of said unit to permit the same to oscillate about the center for lateral-cut records,

and means for converting the movements of said unit into electric impulses.

27. In an electric phonograph reproducer lateral-cut records, electromagnetic-mechanism having a vibratory arma ture, elastic means in pressure contact, with theends'of. said armature for supporting the same in substantially horizontal position,.and a stylus holder connected to the central portion' of said armature and extending laterally therefrom.

28. In an electromagnetic translating instrument, the combination ofa magnet havingypole pieces, a vibratory armature. bar hav ing its ends in operative relationto said pole;

Leoagaet mature and constituting-the sole support for the armature.

ADOLPI-I A. THOMAS. 

